Background: Drug overdose is the leading cause of death among formerly incarcerated adults. Opioid use disorder (OUD) pharmacotherapy (i.e., methadone, buprenorphine, naltrexone) is the most effective treatment, but justice-involved Veterans may have lower access to these medications than other Veterans. Across Department of Veterans Affairs (VA) facilities nationally, in FY2015, 69% of justice-involved Veterans did not receive pharmacotherapy for their OUD. Across facilities, there was variation in the gap between justice- involved and non-justice-involved veterans? receipt of pharmacotherapy; gaps ranged from 15% lower to 42% higher for justice-involved Veterans. The VA is the ideal health care system to address the addiction treatment needs of justice-involved Veterans because of the special services and dedicated funding for these Veterans; however, many Veterans still struggle in the transition from the justice system to health care. Leveraging VA resources, the proposed project will identify unique barriers and facilitators experienced by justice-involved Veterans and evaluate promising implementation strategies to improve access to OUD pharmacotherapy. Given the high risk for overdose and the effectiveness of these medications, it is imperative that we strengthen the transition from the justice system to VA and community health care systems to improve drug addiction treatment and outcomes for justice-involved Veterans. Objectives: Specific aims are to: (1) Quantitatively evaluate patient and facility characteristics associated with differences in receipt of OUD pharmacotherapy among justice-involved Veterans compared to non-justice involved veterans and within-facility changes over time; (2) Qualitatively identify drivers of higher or lower access to OUD pharmacotherapy among justice-involved Veterans compared to other Veterans with OUD at the same facility; (3) Evaluate stakeholders? perceptions of factors that explain within-facility changes in access to OUD pharmacotherapy over time; and (4) Develop and conduct a formative evaluation of implementation strategies to improve access to OUD pharmacotherapy. Methods: Aim 1 will use VA clinical data and mixed effects regression and propensity score methods. In Aims 2-4, 60 qualitative interviews total will be conducted with justice-involved Veterans with OUD and key stakeholders in the criminal justice system, VA and community treatment settings, and VA Justice Programs. The Consolidated Framework for Implementation Research and Stetler et al.?s (2006) formative evaluation strategy will guide qualitative data collection, coding and analysis. Summary: Results will be used to design and select implementation strategies that address identified barriers to test in a future grant, to improve access to OUD pharmacotherapy for justice-involved Veterans. Improving access to drug addiction treatments will help Veterans with OUD achieve recovery and reduce their risk for mortality, recidivism, and other negative health outcomes.